This invention relates generally to electrodes, for example electrocardiograph (ECG) electrodes, and more particularly, to an electrode having a domed contact surface and a method of making and using such domed electrode.
ECG electrodes are well known in the art and are typically placed in direct contact with a patient's skin in the vicinity of the patient's heart. These electrodes can be used to sense the patient's heart functions.
Conventionally, capacitive electrode elements are flat disks which have been stamped or punched from flat sheets of metal. An example of a once commonly used capacitive ECG electrode is described in U.S. Pat. No. 3,882,846 to Fletcher, et al. Fletcher describes an ECG electrode assembly having an insulated electrode element, which is square-shaped, and an impedance transformer contained in a small plastic housing. Fletcher discloses that the electrode element consists of a thin layer of dielectric material deposited by radio frequency sputtering onto a conductive substrate. Also, the impedance transformer includes an operational amplifier with an FET input stage that is configured to provide a low cut-off frequency. Conductive epoxy is used for the wire connection to the substrate and the electrode is attached to the skin with double-sided adhesive tape. The oxide coating can be, among other types listed, tantalum pentoxide and the substrate materials used include silicon.
In conventional stamping processes, the edges of the electrode element typically have no oxide coating. Unless the bare edges are covered prior to use, an ionic condition can occur with the resultant motion artifacts inherent to a conductive electrode element. Stamping can also create significant burs along the edges of the electrode element which could irritate the skin if not removed. Fletcher accounts for both problems by using an insulating resin to cover the edges of the electrode element. The insulating material covers the burs and may prevent any contact between the skin and the bare substrate of the electrode element.
However, a disadvantage of such flat electrode elements is that they can lose contact intermittently with the skin. Particularly under conditions of patient movement, such as lying down or rolling over while sleeping, the flat electrode element may tilt with respect to the surface of the skin. Consequently, much or all of the active electrode surface may lose contact with the skin. Moreover, the use of an insulating resin, adhesive disk or other means to seal the edges of the electrode element, to prevent the aforementioned ionic condition from occurring, only compounds the intermittent contact problem. The insulating material used to cover the edges also can greatly reduce the active surface area of the electrode, thus increasing the likelihood of loss of contact with the skin if the electrode is tilted.
U.S. Pat. No. 5,333,616 to Mills discloses a flat, dry, skin-contacting electrode made from stainless steel which is plated with 3 micron zones of titanium nitride, titanium carbide or titanium carbonitride. However, this electrode is conductive rather than capacitive and the plating is primarily for wear resistance and appearance.
Accordingly, there is a need for an electrode having a domed electrode element wherein the edge is fully coated or shielded so as to prevent the occurrence of an ionic condition and also which has no burs or such burs are sealed from contact with the skin. Such electrode should, at the same time, provide improved and continuous contact with the skin even if the electrode is substantially tilted with respect to the skin.